Bracing for steel platform design
Bracing for steel platform design
(OP)
Hey everyone, I'm designing some platforms for an industrial plant and have a couple questions. I've attached a picture of the platform in STAAD. The platform has a monorail (for a 2.2k load) at the top (36' high) (the longitudinal beam along the center all the way at the top). At the middle elevation a hopper (13.3 kips full) is being supported by the framing. The floor will be diamond plating at this elevation because bags of powder will be stored on the floor and this way powder can fall down below. My question is also about bracing for a frame like this. Since there is not diaphragm at the top does each side of the frame have to be braced? I currently have some bracing to start analysis with because I want to see how it behaves. It's essentially self weight and seismic effect of full hoppers right now.
Thanks
Thanks






RE: Bracing for steel platform design
If you are in a substantial seismic area - the knee braces and diagonal braces ending near mid-height of the columns is probably not a good idea.
Without a diaphragm you either have to brace all sides or add a horizontal system of bracing to establish a stable framework.
Not sure how STAAD works these days graphically (I hated it back in the 1980's)....but your X bracing doesn't appear to be pinned at the ends of the diagonals.
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RE: Bracing for steel platform design
RE: Bracing for steel platform design
RE: Bracing for steel platform design
1) Commonly available.
2) I'll use the same shape everywhere to simplify the mill order.
3) Vertically stiff so no issues with sag/draw.
4) The two side by side bolts that can be installed at the ends of the channels are usually enough. Nice compact gussets.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Bracing for steel platform design
RE: Bracing for steel platform design
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Bracing for steel platform design
RE: Bracing for steel platform design
If it were my design, I would eliminate:
1) Six of the eight knee braces for the very lowest platform. For most of the lateral degrees of freedom in that platform, I'd let the platform ride along with the two columns that go full height.
2) The knee brace in the foreground right above the lowest platform.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Bracing for steel platform design
RE: Bracing for steel platform design
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Bracing for steel platform design
RE: Bracing for steel platform design
Why not make the Z-axis (transverse) as moment side and X-axis (longitudinal) braced side? Making this will also give the monorail crane load transfer to the column flange by moment connection which is same as for the equipment below. It is easier to have moment connection at the column flanges.
Also, in lieu of the mid height bracing, along X-axis, could you not make it a Chevron brace?
RE: Bracing for steel platform design
I thought about the moment connections in the short direction. Especially with the limitations on bracing. I considered the cost of moment connection vs. a tab connection and kicker and thought the gussets for the kickers would be shop welded and you just bolt up the kicker, but there are several of them. But with all the restrictions coming into play, the moment connection might be the best. Put moment connections at the two ends of the frame (or at least the one end where the fork lift pulls in) in the short direction at all levels and transfer load via horizontal braces.
I wanted to make this bracing a Chevron, but they need clearance to pull in with a forklift to load the sack (along short direction). The forklift pulls in through the front at the short direction and there is a hatch that opens and monorail lowers to pick up bag. As for the long direction, I also wanted to use a Chevron (and am still fighting for this because you need a lateral resisting system) but apparently they have a rule that if there is bracing in a bay no one can walk through that bay. Doesn't entirely make sense to me since a Chevron would give you plenty of space to walk through.
RE: Bracing for steel platform design
Safety. Workers would bump their heads on the bracing unless you provide a system to guide them appropriately.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Bracing for steel platform design
RE: Bracing for steel platform design
Or alternative solution to eliminate the remaining four (4) knee braces is by using again a moment connection especially the girder near the equipment.
In the case of the mid-height bracing, if it is not possible to use Chevron as you said, then just make sure your mid-height it works in your analysis.
RE: Bracing for steel platform design